This invention relates to a new and useful improvement in multi-flapper check valves.
In flapper valves of the design disclosed in WBrovo, U.S. Pat. No. 1,238,878 (1917), and improved upon by wheeler in U.S. Pat. Nos. 3,007,488 (1961), 3,026,901 (1962), 3,072,141 (1963), and 3,074,427 (1963), the plate bearings or hinges contact; and, when the valve is oriented for horizontal flow conditions with the rib in a vertical position, the hinge or hinges of one plate (the "upper" plate) rest on the hinge or hinges of the other plate (the "lower" plate). This additional loading of the hinge of the lower plate increases the frictional force to be overcome in closing the lower plate. This results in a disparity between the forces necessary to close the upper plate and the lower plate, with the lower plate requiring significantly more force to effect closure. Particularly in larger valves of this design, the frictional forces can become so great as to cause the lower plate to stop or hesitate before closing, thereby impairing valve response and resulting in pressure surges upon closure.
This problem can be avoided by mounting the hinges for the upper plate and the lower plate on separate shafts, as was done in Smith, U.S. Pat. No. 3,384,112 (1968). However, the problem is solved by the present invention, which still permits the use of a single hinge pin for both upper and lower plates, rather than separate hinge pins for each of the two plates.
To improve the response time of the check valve, it is desirable to reduce the frictional loading of the lower plate hinge, thereby reducing the amount of force necessary to close the lower plate. A reduction in the frictional forces acting on the lower plate will allow the plate to close more quickly, thus improving the valve response and reducing the pressure surges and "hammer" associated with poor valve response. The addition of bearings or washers between the hinges may reduce the effective coefficient of friction, and thereby reduce the amount of force necessary to operate the lower plate. However, the additional loading of the hinge of the lower plate will still impair the operation of the lower plate.
Accordingly, it is an object of the present invention to provide a multi-flapper check valve wherein each plate is independently supported.
Another object of this invention is to provide a multi-flapper check valve with improved valve response.
A further object of this invention is to provide a multi-flapper check valve wherein the force necessary to close the lower plate is reduced.
Other objects and purposes of this invention will appear from the following descriptions, examples, and claims.